Many types of devices have been developed over the years for the purpose of converting liquids or aerosols into gas-phase fluids. Some such devices have been developed, for example, to discharge small droplets from an inhaler-type medicinal administration apparatus.
Typical inhalers include a pressurized canister with measured doses of medication inside. Squeezing the top of the canister converts liquid medication into an inhalable mist. Inhalers enable children and adults to deliver medicine directly to their lungs. Typical aerosol inhalers usually comprise a diverging nozzle at an outlet to the pressurized liquid, which tends to vaporize the liquid medicine to a droplet volume median diameter on the order of 50 μm.
50 μm particles produced by typical inhalers can effectively treat certain lung ailments. For example, bronchodilators such as albuterol treat acute asthma by causing the lung passages to open or dilate. Similarly, nebulizers typically vaporize liquid medications to a droplet volume median diameter on the order of 50 μm. However, in addition to direct lung treatments, applicant notes that liquid medicinal drugs could also be delivered directly to the bloodstream through the lungs.
The lungs include groups of tiny air sacs called alveoli. The alveoli have very thin walls or membranes, and small blood vessels called capillaries run through these membranes. Oxygen molecules are small enough to pass through the membranes and into the blood in the capillaries. Other particles having diameters of approximately 1 to 3 μm or smaller may also pass through the alveoli membranes and directly into the blood stream. Nevertheless, there are currently no efficient methods of reducing liquids to particle sizes small enough to pass through the alveoli membranes.
In addition, typical aerosol inhalers produce a wide range of particle droplet sizes, and much of the metered medication tends to simply impinge the mouth or the back of the throat of a user. Consequently, sometimes only a fraction of the medication is deeply inhaled.